class code1 {
    //单词搜索
    boolean[][] vis;
    int m,n;
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};
    public boolean exist(char[][] board, String word) {
        m = board.length;
        n = board[0].length;
        vis = new boolean[m][n];

        //找到第一个匹配的位置
        for(int i=0;i<m;i++) {
            for(int j=0;j<n;j++) {
                if(board[i][j]==word.charAt(0)) {
                    vis[i][j] = true;
                    if(dfs(board,i,j,word,1)) return true;
                    vis[i][j] = false;
                }
            }
        }
        return false;
    }

    boolean dfs(char[][] board,int i,int j, String word,int pos) {
        //出口
        if(pos==word.length()) {
            return true;
        }

        for(int k=0;k<4;k++) {
            int x = i+dx[k];
            int y = j+dy[k];
            if(x>=0 && x<m && y>=0 && y<n && !vis[x][y] && board[x][y]==word.charAt(pos)) {
                vis[x][y] = true;
                if(dfs(board,x,y,word,pos+1)) return true;
                vis[x][y] = false;
            }
        }
        return false;
    }
}